The implementation of various relay techniques is described in 3rd Generation Partnership Project (3GPP) Long Term Evolution Advanced (LTE-A) standards as a potential solution for providing cost-efficient delivery of high data transmission rates. As described, such techniques generally involve the use of a low-power, low-cost relay node (RN) that typically does not require wired backhaul access. Such RNs can not only offer high flexibility in their placement, but also facilitate fast, on-demand network rollout. Appropriate deployment of RNs can enlarge coverage areas, increase system throughput, reduce mobile power consumption, support group mobility, and simplify temporary network deployment. An additional benefit is the provision of a uniform end-user experience for both cell-center and cell-edge users.
Known approaches to the use of different types of relays are dependent upon the various functionalities each RN supports. The RNs are attached to the packet core network via an evolved Node B (eNB), which is referred to as Donor eNB. For example, LTE-A defines two types of RNs. A Type I RN behaves as a mini base station having full radio resource control. It has its own physical cell identifier and appears as an independent cell to the user equipment (UE) and transmits its own pilot/control signals. Conversely, a Type II RN has neither its own physical cell identifier nor does it transmit pilot/control signals. Furthermore, a Type II RN does not have any radio resource scheduling functionalities and only helps the evolved Node B (eNB) with data transmission. Accordingly, the donor eNB is responsible for scheduling schedule the packet transmissions to or from a Type II RN.
In an LTE network, each eNB identifies itself by broadcasting a unique signature sequence, called cell-specific reference signal (CRS). The CRS is a pseudo-random sequence generated as a function of its Cell ID. The resource elements used for CRS transmission also depend on its Cell ID. When selecting the serving cell, the UE measures the reference signal received power (RSRP) (i.e., the received signal power of CRS), a reference signal received quality (RSRQ), or both, from neighboring cells and the UE typically picks the strongest cell as the serving cell. The fact that a Type II RN has neither a cell ID nor broadcasts CRS results in the relay node becoming a hidden node during a serving cell selection process. As a result, a UE device selects its serving cell based on the observed signal strengths from the eNBs only and does not consider the signals from Type II relay nodes.